Disposable absorbent products have been known for some time, including such products as disposable diapers, sanitary napkins, wound dressings, bandages, incontinent pads, and the like. Such products generally incorporate absorbent structures containing superabsorbent material which absorbs and retains large quantities of liquid, even under load, large quantities of liquids. In order for superabsorbent material to function, the liquid being absorbed in the absorbent structure must be transported to the superabsorbent material. In other words, the superabsorbent material must be placed in a position to be contacted by liquid. Furthermore, as the superabsorbent material absorbs the liquid, it must be allowed to swell. If the superabsorbent material is prevented from swelling, it will cease absorbing liquids. Hence if the superabsorbent material is to function in diapers and sanitary napkins wherein the liquid to be absorbed is placed in a small void area, the structure of the absorbent layer containing superabsorbent materials, generally comprised of a mixture of hydrophilic fibers and superabsorbent materials, appears to be critical.
Over the years a number of techniques have been disclosed in an attempt to provide absorbent structures which make efficient use of the superabsorbent material. U.S. Pat. No. 4,673,402 to Weisman et al. discloses a dual-layer absorbent core wherein an absorbent acquisition layer overlays a lower fluid storage area which is preferably placed in the front two-thirds section of the absorbent core. U.S. Pat. No. 4,834,735 to Alemany et al. discloses an absorbent member wherein there is formed a liquid acquisition zone having a relatively low concentration of superabsorbent material in the front area of typical liquid deposition. U.S. Pat. No. 4,699,823 discloses an absorbent layer wherein superabsorbent particles are disposed to form a substantially continuous, non-stepwise, positive concentration gradient of superabsorbent in a thickness direction of the layer.
The aforementioned prior art has been directed toward forming a concentration gradient of superabsorbent within the absorbent structures to improve the liquid diffusion process in the absorbent structures while reducing possibilities for gel blocking to take place. Gel blocking occurs when superabsorbent particles are sufficiently close together that as they swell a layer of gel is formed and additional liquid can not penetrate that layer. These approaches are however not very effective in improving rewet properties of the absorbent structure. The term rewet describes a phenomenon that occurs when some pressure is exerted onto an absorbent layer, liquids absorbed in that layer flow or strike back to and rewet the top surface of the layer.
U.S. Pat. Nos. 4,608,292 and 4,701,237 to Lassen disclose an absorbent web wherein apertures are formed within the web to increase the available area for liquid absorption by superabsorbent. Another example of such an approach is disclosed in U.S. Pat. No. 4,676,784 to Erdman et al. Although the apertures are effective in that they provide passages for liquids to go through, they also permit liquids to strike back to a top surface of the structure, which produce a poor rewet property.